This research is concerned with two main project areas: 1) hormonal control of behavior in the rat, and 2) ultrasonic vocalizations and sexual behavior of rats. Specifically, the following investigations will be carried out: 1) the influence of various sex steroids and their metabolites on the agonistic behavior of the rat; 2) sites of action of sex hormones in the brain in the regulation of agonistic and sexual behavior in rats; 3) effects of the ultrasonic vocalizations of male rats on the reproductive behavior and physiology of female rats. In the last, there is a particular interest in whether vocalizations function to modulate the reproductive response to mating in rats and/or whether behavioral effects are evident. BIBLIOGRAPHIC REFERENCES: Barfield, R.J. and L.A. Geyer, 1975. The ultrasonic postejaculatory vocalization and the postejaculatory refractory period of the male rat. J. comp. physiol. Psychol., 88:723-734. Barfield, R.J., C. Wilson, & P.G. McDonald, 1975. Sexual behavior: Extreme reduction of postejaculatory refractory period by midbrain lesions in male rats. Science 189: 147-149.